The phosphomannose isomerase (pmi) gene of Escherichia coli was cloned on a broad-host-range cosmid vector and expressed in Pseudomonas aeruginosa at a low level. Plasmid pAD3, which harbors the E. coli pmi gene, contains a 6.2-kilobase-pair HindmI fragment derived from the chromosome of E. coli. Subcloning produced plasmids carrying the 1.5-kilobase-pair HindlII-HpaI subfragment of pAD3 that restored alginic acid production in a nonmucoid, alginate-negative mutant of P. aeruginosa. This fragment also complemented mannose-negative, phosphomannose isomerase-negative mutants of E. coli and showed no homology by DNA-DNA hybridization to P. aeruginosa chromosomal DNA. By using a BamHI constructed cosmid clone bank of the stable alginate producing strain 8830, we have been able to isolate a recombinant plasmid of P. aeruginosa origin that also restores alginate production in the alginate-negative mutant. This new recombinant
Non-motile mutants of Vibrio cholerae were isolated after transposon insertion mutagenesis with either Tn5 on a plasmid or TnlOptac mini-kan in bacteriophage 1. The physical location and number of transposon insertions was determined. Eighteen Tn5 insertion mutants and 11 TnlOptuc mini-kan insertion mutants had single unique insertion sites. The 18 Tn5 insertions were contained within six different EcoRI fragments and the 11 TnlOptac mini-kan insertions were contained within eight different fragments of V. cholerae chromosomal DNA. These data suggest that multiple genes are involved in motility. Immunoblot analysis of nonmotile mutants with antibody to wild-type flagellar core protein indicated that two of the nonmotile mutants made flagellar core protein. Three additional mutants redc%ed weakly with the antibodies. However, thee mutants with immunopositive reactions did not produce any structures which resembled flagella by tranhissbm electron microscopy. In addition, none of the other nonmotile mutants produced wild-type flagella.-However, five mutants which did not react in the immunoblot produced a structure which resembled a flagellar sheath without the internal flagellar core. In addition to having no filamentous core, the sheaths often extended from the sides of the bacteria, rather than from the poles where the flagellum is normally located. The data suggest thait sheath formation is independent of flagellar filament formation, but that proper positioning of the sheath may require the flagellar filament.
Though there has been widespread enthusiasm to leverage technology to strengthen low-resource classrooms, to date very few programs have documented rigorous benefits from such interventions. In this paper, we describe an exploratory evaluation of the use of pre-packaged electronic teaching aids, consisting of presentation slides and multimedia content, in a government school in peri-urban India. Via a small-scale randomized controlled trial, encompassing 2 subjects, 72 students, and a 3-week intervention, we measure the impact of the electronic content on learning outcomes. In one subject (English), we find that the intervention significantly increases student scores, measured both by a custom exam as well as a standard unit test in the school. However, in another subject (science), we do not find any evidence for learning benefits. Despite its small scale, this study shows that it is possible to bolster learning in low-resource schools via use of electronic teaching aids, thereby justifying investment in larger scale trials in the future.
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